EXAMINING REEF MOUND CONSTRUCTION TO UNDERSTAND HOW REEFS RECOVERED AFTER MASS EXTINCTION

The end Permian mass extinction decimated reef communities within the Panthalassa and Tethys Ocean. Following the extinction, reef communities recovered in four progressive stages: the stabilization, colonization, diversification and domination stages (Flügel, 1982). Previous research focused on Tethys Ocean reef studies leaving Panthalassan reefs understudied. This study focuses on Northeastern Panthalassan reefs and describes four new reefs ranging between 1m and 4m in height, occurring on a depressed shale bed. Bonuso et al., (2018) categorized their Northeastern Panthalassan reefs into the colonization stage of reef recovery based on the observation that biostromes and a reef mound contain large amounts of micrite built by low-growing binders and encrusting organisms. The present study aims to test the hypothesis that the colonization stage best describes the four reefs which are the subject of this study. To test this hypothesis, we examined thin sections from each reef and point counted fossils and the mineral matrix. We found the dominant component of each reef mound to be mineral matrix, indicating they are uniformly matrix supported communities. The reef mound TR1 contains 43% biomass, TR2: 38%, TR3: 32% and TR4: 46% biomass. The biomass of each reef was overwhelmingly dominated by several distinct varieties of non-identifiable branching sponges. TR1’s biomass was 96% sponge, 94% for TR2, 98% for TR3 and 100% for TR4. The remaining organisms within the reef mounds consisted of sparsely populated bivalves, brachiopods, echinoderms and gastropods. Since the reefs contain matrix supported branching sponges, encrusting growth habits, and lack framework builders, we interpreted the reefs as sponge reef mounds within the colonization stage of reef recovery.

Bonuso, N., Loyd, S., Lorentz, N.J., 2018. Pioneer reef communities within a Middle Triassic (Anisian) to Upper Triassic (Carnian) mixed carbonate-siliciclastic ramp system from the Star Peak Group, South Canyon, central Nevada. Palaeogeography, Palaeoclimatology, Palaeoecology 503, 1-12.

Flügel, Erik, 1982, Microfacies of Carbonate Rocks: Analysis, Interpretation and Application: Berlin, Heidelberg, New York, Springer, 830 p.